The electric guitar is fundamentally an analog instrument, and its electrical design has not changed appreciably over the last 50 years. With the advent of low-cost processing and computers, the ability to provide sophisticated musical interfaces has made exponential progress over the same time period. The advantages that this technology can bring to the music world is well established in the keyboard world, where pianos have been transformed from a purely mechanical instrument into sophisticated music generators capable of sounding like any other instrument. Costs have plummeted to where an electronic keyboard is available as an inexpensive consumer product. The same can not be said to be true in the guitar world.
One of the main reasons that guitars have not entered into the digital world to the extent that pianos have has to with the fact that piano keys can be thought of as switches, and so adapt well to a digital interface. In contrast, an electric guitar relies on the vibration of a metal string across an electromagnetic pickup in order to produce an analog signal.
There are existing guitars that convert this analog signal into a digital form that can then be used to interface to digital processors. The musical instrument digital interface (MIDI) is standard format in musical electronics, and there are a number of MIDI guitars currently available. However, these have some fundamental flaws that prevent the guitars from providing an authentic feel and sound to the musician.
The principal problem is that in order to convert from the analog form to a digital one, the frequency of the string must be determined, which takes some perceptible amount of time. This delay or latency is very distracting to a musician attempting to play the guitar since the audio feedback is delayed from the time the desired note is struck until the sound is heard. The problem gets worse with lower frequencies as the corresponding periods become longer. The fact that the amount of latency varies considerably across the guitar note spectrum is another aspect of this problem that requires adaptation on the part of the player.
In addition to the frequency, a MIDI note event also includes a parameter for velocity or volume. In a keyboard, this represents how fast, or how hard a key was struck. In existing digital guitar methods such as those described above, there are additional problems in accurately determining the volume of the note. There is again a finite time that must elapse before this determination can be made, which can cause additional delays on top of the frequency determination. Since both the frequency and the volume information have to be released together to form a MIDI code, the delay becomes the worst of both.
Both the volume and frequency determination of the note are also prone to many errors, because there are many overtones in a guitar signal that combine to make these processes difficult. For example, ambient noise pickup (typically 60 cycle “hum”) or a variety of other factors may cause false notes.
Another problem with existing digital guitars is capturing certain expression nuances. For example, an important element of playing guitar is note bending, or changing the pitch of a note by stretching the guitar string after it is initially played. Since the pitch of the note is constantly changing, the problem of converting this in real time to a digital signal becomes impractical. Other expression nuances include hammer-ons, pull-offs, and producing vibrato.
In order to accomplish the goal of a digital interface without latency, some systems use the fret board of the guitar as a switch matrix input, similar to a keyboard. Various techniques have been employed to form a switch matrix. One is to actually install a series of push-button switches on the fingerboard. This approach does not use guitar strings and requires a substantial adaptation of playing style, without allowing for the capture of expression nuances.
Another technique that has been used takes advantage of the fact that the guitar strings are metal, and electrically conductive, as are the fret bars located on the guitar neck. As the strings are fretted by the player, a contact is made and can be read. It is necessary in this case to produce special fret bars that are separated into six segments in order to distinguish a unique contact when all strings are fretted across and a common bus is formed. This method is expensive to manufacture and is incapable of capturing expression nuances.